JP2010273249A - Sidetone cancellation method and sidetone canceler - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a pseudo sidetone from being caused when a speech is made using any other device in a state that a device such as a telephone set which generates sidetones is not connected or a device such as a telephone set is not in a speech state. <P>SOLUTION: A sidetone canceler 101 comprises: a variable filter section 102 for filtering a transmission signal x(t); a subtractor 104 for subtracting the output signal y'(t) of the variable filter section 102 from a reception signal y(t); a filter coefficient updating section 103 for updating the filter coefficient of the variable filter section 102 so as to reduce the mean square of the sidetone that is a transmission signal component included in the reception signal y(t); a sidetone detection section 105 for detecting presence/no presence of the sidetone on the basis of the filter coefficient; and a switch section 106 for selecting a signal e(t) when presence of the sidetone is determined and for selecting the receive signal y(t) when absence of the sidetone is determined. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a side-tone canceling method and a side-tone canceller in an audio conference or the like performed by connecting a hands-free device instead of a telephone handset.

  A conventional side tone canceller will be described. FIG. 10 is a block diagram showing a configuration of a conventional sidetone canceller disclosed in Non-Patent Document 1. The side tone canceller 802 is obtained by applying an adaptive filter to side tone cancellation, and includes a variable filter unit 102, a filter coefficient update unit 103, and a subtraction unit 104.

  FIG. 11 is a diagram for explaining the operation of the sidetone canceller, and is a diagram showing how to use the hands-free device to which the sidetone canceller is applied. The hands-free device 702 is connected to the handset connection terminal 705 of the telephone 701 and can be used as a substitute for the handset of the telephone 701. Further, the hands-free device 702 is also connected to the TV conference device 703 and the like. You can make a call at the same time.

  FIG. 12 is a diagram illustrating a signal flow when the connection of FIG. 11 is performed. The telephone set 701 has a side tone adding circuit 801 for returning the transmitted voice to the receiving side in order to reduce the feeling of blockage of the ear when using the handset. However, in the hands-free call with no sense of blockage of the ear, side sounds are unnecessary and can cause howling. Therefore, it is necessary to eliminate the side sounds. The side tone canceller 802 is used to erase the side tone.

  In addition to the side-tone canceller 802, the hands-free device 702 includes an acoustic echo canceller 804 that eliminates acoustic echo that sounds from the speaker 708 to the microphone 709, a terminal 706 for connecting a telephone, and a terminal 707 for connecting a normal device. And a mixing unit 803 for mixing signals so that both can be used simultaneously. The mixing unit 803 mixes the transmission signal from the telephone 701 and the transmission signal from the TV conference device 703 and sends the mixed signal to the speaker 708, and the reception signal collected by the microphone 709 and the transmission from the TV conference device 703. The signal is mixed and sent to the telephone set 701. In addition, the mixing unit 803 mixes the transmission signal from the telephone set 701 and the reception signal collected by the microphone 709 and sends the mixed signal to the TV conference device 703.

  Next, the side tone canceller 802 will be described in detail with reference to FIG. Sidetone canceller 802 receives reception signal y (t) from telephone set 701 and transmission signal x (t) sent from mixing unit 803 to telephone set 701, and deletes sidetone components from reception signal y (t). The signal e (t) is output to the mixing unit 803. However, t represents time.

The variable filter unit 102 filters the transmission signal x (t) transmitted to the telephone set 701 with the filter coefficient H (t) and outputs a pseudo side sound signal y ′ (t). The subtracting unit 104 subtracts the pseudo side sound signal y ′ (t) from the reception signal y (t) from the telephone set 701 and outputs a signal e (t) obtained by eliminating the side sound component from the reception signal y (t). . The filter coefficient H (t) is a vector of filter coefficients at time t, and H (t) = (h (0, t), h (1, t),..., H (L−1, t). ) ^Represented by ^T. h (i, t) is the filter coefficient of the i-th tap at time t, and L is the tap length of the filter.

The filter coefficient updating unit 103 receives a signal e (t) from which side sound components are eliminated from the transmission signal x (t) and the reception signal y (t), and uses a NLMS (Normalized Least Mean Square) algorithm as a filter. The coefficient is updated, and the filter coefficient is updated so that the side sound is deleted. The update formula of the NLMS method is represented by the formula (1).
H (t + 1) = H (t) + a · X (t) · e (t) / X (t) ^T X (t) (1)

However, a is a preset step size and takes a value of 0 <a <2. X (t) is a vector of L samples of the received signal y (t) at time t, and X (t) = (x (t-0), x (t-1),..., X (T−L + 1)) ^T By the above processing, the side sound included in the received signal y (t) is deleted.

Simon Heykin, “Introduction to Adaptive Filters”, 3rd edition, Hyundai Engineering Co., Ltd., ISBN 4-87472-134-6, p. 120-121, 1987

  When the telephone is not connected or when the telephone is not in a talking state, no side sound is generated. However, in the conventional side tone canceller, the filter coefficient H (t) is not completely zero due to the noise component included in the received signal y (t) and the calculation accuracy of the computer. (T) is not 0. For this reason, when a call is made using a normal device connection terminal, the pseudo-side sound signal y ′ (t) is input to the mixing unit, thereby degrading the quality of the call.

  As described above, in the conventional side tone canceller, when the phone is not connected or the phone is not in a call state, the side tone canceller is simulated when a call is performed using a normal device connection terminal. Since a side sound is generated, there is a problem that it sounds as if the side sound has returned during a call.

  It is an object of the present invention to provide a pseudo side sound when a phone call is made using another device in a state where a device such as a phone that generates a side tone is not connected or a device such as a phone is not in a call state. It is to provide a side tone canceller that does not generate a voice and to improve call quality.

  The sidetone canceling method of the present invention includes a variable filter procedure for filtering a transmission signal to be transmitted to a call partner with a set filter coefficient, and subtracting an output signal obtained by the variable filter procedure from a reception signal from the call partner And the variable filter procedure so that the mean square of the side tone, which is the transmission signal component included in the received signal, is reduced based on the subtraction procedure to be performed and the transmission signal and the output signal obtained by the subtraction procedure. A filter coefficient update procedure for sequentially updating the filter coefficient of the side filter, a side sound detection procedure for detecting the presence or absence of the side sound based on the filter coefficient of the variable filter procedure, and the detection result of the side sound detection procedure includes a side sound. If there is a switch, the output signal obtained in the subtraction procedure is selected and output. It is characterized in further comprising and.

Further, in one configuration example of the sidetone canceling method of the present invention, the sidetone detection procedure includes an absolute value calculation procedure for calculating an absolute value of a filter coefficient of the variable filter procedure, and a maximum value of the absolute value of the filter coefficient. The maximum value detection procedure for obtaining the maximum threshold value is compared with a preset fixed threshold value and the maximum value is determined. If the maximum value is larger than the fixed threshold value, it is determined that there is a side sound. In this case, a fixed threshold value comparison procedure for determining that there is no side sound is included.
Further, in one configuration example of the sidetone canceling method of the present invention, the sidetone detection procedure includes an absolute value calculation procedure for calculating an absolute value of the filter coefficient of the variable filter procedure, and a maximum value of the absolute value of the filter coefficient. A maximum value detection procedure for obtaining, an average value calculation procedure for calculating an average value of absolute values of the filter coefficients, a threshold value setting procedure for setting a value obtained by multiplying the average value by a preset constant as a threshold value, A threshold comparison procedure that compares a threshold value with the maximum value, determines that there is a side sound when the maximum value is greater than the threshold value, and determines that there is no side sound when the maximum value is less than or equal to the threshold value. It is characterized by this.

In addition, one configuration example of the sidetone canceling method of the present invention further includes a filter coefficient reset for setting the filter coefficient of the variable filter procedure to 0 when the sidetone is present and the sidetone is absent. A procedure is provided.
In the configuration example of the sidetone cancellation method of the present invention, the filter coefficient reset procedure includes a first level calculation procedure for calculating a level of the output signal obtained by the subtraction procedure, and a level of the received signal. A second level calculation procedure for calculating, a constant multiplication procedure for multiplying the level of the received signal by a preset constant, the level of the output signal obtained by the constant multiplication procedure, and the output signal obtained by the subtraction procedure And a comparison procedure for setting the filter coefficient of the variable filter procedure to 0 when the level of the output signal obtained by the subtraction procedure is larger.

  Further, the sidetone canceller of the present invention includes variable filter means for filtering a transmission signal to be transmitted to a call partner with a set filter coefficient, and subtraction for subtracting an output signal of the variable filter means from a reception signal from the call partner. And, based on the transmission signal and the output signal of the subtracting means, the filter coefficients of the variable filter means are successively set so that the mean square of the side tone, which is the transmission signal component included in the reception signal, becomes small. A filter coefficient updating means for updating, a side sound detecting means for detecting the presence or absence of the side sound based on a filter coefficient of the variable filter means, and when the detection result of the side sound detection means is a side sound, Switch means for selecting and outputting the reception signal when the output signal of the subtraction means is selected and output, and the detection result is that there is no side sound. It is intended to.

  In the present invention, a side-tone detection procedure and a switch procedure are added to the conventional side-tone cancellation method, and when the detection result of the side-tone detection procedure includes a side tone, the output signal obtained by the subtraction procedure, That is, a signal with a side sound canceled is selected and output. If the detection result is that there is no side sound, a received signal, that is, a signal before the side sound is canceled is selected and output. As a result, according to the present invention, when a device such as a telephone that generates a side sound is not connected to the own device (for example, a hands-free device) or a device such as a telephone is not in a talking state, another device is used. When a call is made, it is possible to prevent the side sound from being heard on the speaker of the own device or another device side.

  Further, in the present invention, the absolute value of the filter coefficient of the variable filter procedure is calculated, the maximum value of the absolute value of the filter coefficient is obtained, and when the maximum value is larger than a preset fixed threshold, it is determined that there is a side sound. To detect. As a result, in the present invention, when a device such as a telephone that generates a side sound is not connected to the own device or when a device such as a telephone is not in a talking state, the received signal before canceling the side sound is displayed. It is possible to output, and generation of unnecessary pseudo side sounds can be suppressed.

  In the present invention, the threshold in the sidetone detection procedure is a value obtained by multiplying the average value of the absolute value of the filter coefficient by a preset constant, and the maximum value of the absolute value of the filter coefficient is compared. By detecting that there is a side sound when the value is larger, the side sound can be detected regardless of the size of the side sound. As a result, in the present invention, it is possible to detect the presence or absence of a side sound even when a device such as a telephone with a non-common side sound level is connected to the device, and the side sound canceller can be operated normally. Can do.

  Further, in the present invention, the filter coefficient of the variable filter procedure is set to 0 when shifting from a state where there is a side sound to a state where there is no side sound. As a result, in the present invention, there is no side sound (a device such as a phone that generates a side sound) from a state where a side sound is present (a device such as a phone that generates a side sound is connected to the own device). When the process shifts to a state in which the side sound is not connected, the generation of the pseudo side sound can be stopped immediately, and the phenomenon that the side sound is heard to be returned can be prevented.

It is a block diagram which shows the structure of the sidetone canceller which concerns on the 1st Embodiment of this invention. It is a flowchart which shows the operation | movement of the variable filter part of the side sound canceller which concerns on the 1st Embodiment of this invention, a filter coefficient update part, and a subtraction part, and the operation | movement of a side sound detection part and a switch part. It is a block diagram which shows the structure of the side sound detection part of the side sound canceller which concerns on the 1st Embodiment of this invention. It is a flowchart which shows operation | movement of the side-tone detection part of the side-tone canceller which concerns on the 1st Embodiment of this invention. It is a block diagram which shows the structure of the side sound detection part of the side sound canceller which concerns on the 2nd Embodiment of this invention. It is a flowchart which shows operation | movement of the side-tone detection part of the side-tone canceller based on the 2nd Embodiment of this invention. It is a block diagram which shows the structure of the sidetone canceller which concerns on the 3rd Embodiment of this invention. It is a block diagram which shows the structure of the filter coefficient reset part of the side tone canceller which concerns on the 3rd Embodiment of this invention. It is a flowchart which shows operation | movement of the filter coefficient reset part of the sidetone canceller which concerns on the 3rd Embodiment of this invention. It is a block diagram which shows the structure of the conventional sidetone cancellation apparatus. It is a figure explaining the usage method of the hands-free apparatus which is an application destination of a side tone canceller. It is a figure which shows the flow of a signal at the time of performing the connection of FIG.

[First Embodiment]
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the configuration of a sidetone canceller according to the first embodiment of the present invention.
Sidetone canceller 101 according to the present embodiment includes variable filter section 102, filter coefficient update section 103, subtraction section 104, sidetone detection section 105, and switch section 106.

  2A is a flowchart showing the operations of the variable filter unit 102, the filter coefficient updating unit 103, and the subtraction unit 104, and FIG. 2B is a flowchart showing the operations of the side sound detection unit 105 and the switch unit 106.

  The variable filter unit 102 filters the transmission signal x (t) transmitted to the telephone with the filter coefficient H (t) and outputs the pseudo side sound signal y ′ (t) (step S100 in FIG. 2A). The subtraction unit 104 subtracts the pseudo side sound signal y ′ (t) from the reception signal y (t) from the telephone, and outputs a signal e (t) obtained by eliminating the side sound component from the reception signal y (t) ( Step S101). Based on the transmission signal x (t) and the output signal e (t) of the subtraction unit 104, the filter coefficient updating unit 103 reduces the mean square of the side sound included in the reception signal y (t). The filter coefficient H (t) of the variable filter unit 102 is sequentially updated (step S102). Since the operations of the variable filter unit 102, the filter coefficient update unit 103, and the subtraction unit 104 are the same as those of the conventional side tone canceller, detailed description thereof is omitted.

  The side sound detection unit 105 detects the presence or absence of a side sound (FIG. 2B, step S103), and if the detection result is that there is a side sound (YES in step S104), the switch unit 106 includes a subtraction unit 104. Output signal e (t) is selected and output (step S105), and if the detection result is that there is no side sound (NO in step S104), the received signal y (t) is selected for the switch unit 106. To output (step S106). Hereinafter, operations of the side sound detection unit 105 and the switch unit 106 will be described in more detail.

  The side-tone detection unit 105 determines from the filter coefficient H (t) of the variable filter unit 102 whether there is a side-tone, that is, a device (hands-free device) that includes the side-tone canceller generates a side-tone (phone connection device). A device such as a telephone connected to a terminal) is detected. FIG. 3 is a block diagram showing the configuration of the side sound detection unit 105, and FIG. 4 is a flowchart showing the operation of the side sound detection unit 105. The side tone detection unit 105 of the present embodiment includes an absolute value calculation unit 201, a maximum value detection unit 202, and a fixed threshold value comparison unit 203.

The absolute value calculation unit 201 calculates the absolute value F (t) of the filter coefficient H (t) of the variable filter unit 102 (step S200 in FIG. 4). The calculation process of the absolute value calculation unit 201 is expressed by Expression (2). However, | x | represents taking the absolute value of x.
F (t) = | H (t) | (2)

Next, the maximum value detection unit 202 detects the maximum value Fm (t) of the absolute value F (t) of the filter coefficient H (t) calculated by the absolute value calculation unit 201 (step S201). The processing of the maximum value detection unit 202 is expressed by Expression (3). However, max (Z) means taking the maximum value among the elements of the vector Z.
Fm (t) = max (F (t)) (3)

  Next, the fixed threshold value comparison unit 203 compares the maximum value Fm (t) detected by the maximum value detection unit 202 with a preset fixed threshold value G (step S202), and the maximum value Fm (t) is fixed. If it is larger than the threshold G, it is determined that there is a side sound, that is, the own device is connected to a device such as a telephone that generates the side sound (step S203), and the maximum value Fm (t) is equal to or less than the fixed threshold G. In this case, it is determined that there is no side sound, that is, the apparatus is not connected to a device that generates side sound (step S204). Here, the fixed threshold value G is set to a value sufficiently smaller than the normally assumed side-tone transmission path gain. Usually, G is in the range of about 0.01 to 0.2. Then, the fixed threshold value comparison unit 203 outputs the detection result of the presence or absence of side sounds to the switch unit 106 (step S205).

  The switch unit 106 selects either the reception signal y (t) or the output signal e (t) of the subtraction unit 104 according to the detection result of the side sound detection unit 105 and outputs it as the output signal z (t). . The switch unit 106 selects and outputs the output signal e (t) of the subtracting unit 104 when the detection result of the side sound detecting unit 105 indicates that there is a side sound (step S105 in FIG. 2B). If the detection result is that there is no side sound, the received signal y (t) is selected and output (step S106). The output signal z (t) of the switch unit 106 is sent to the mixing unit described with reference to FIG.

  As described above, in the present embodiment, by providing the side sound detection unit 105 and the switch unit 106, when a device such as a telephone that generates a side sound is not connected to its own device, The received signal before being subjected to removal processing can be output as it is, and it is possible to prevent the pseudo side sound from being sent to the mixing unit. Further, when a device that generates a side sound is connected to the own apparatus, it is possible to output a reception signal after the side sound is removed and buried. As a result, in this embodiment, when a call is performed using a normal device connection terminal in a state where the telephone is not connected or the telephone is not in a call state, It is possible to prevent a side sound from being heard as if it is returning on the device side such as a TV conference device connected to a normal device connection terminal.

[Second Embodiment]
Next, a second embodiment of the present invention will be described. FIG. 5 is a block diagram showing the configuration of the side tone detection unit of the side tone canceller according to the second embodiment of the present invention, and FIG. 6 is a flowchart showing the operation of the side tone detection unit. In the sidetone canceller of the present embodiment, the sidetone detection unit 105 of the first embodiment is configured as shown in FIG. The overall configuration of the sidetone canceller of the present embodiment is the same as that shown in the block diagram of FIG. 1, and includes a variable filter unit 102, a filter coefficient update unit 103, a subtraction unit 104, a sidetone detection unit 105, And a switch unit 106. Since the variable filter unit 102, the filter coefficient update unit 103, the subtraction unit 104, and the switch unit 106 are the same as the sidetone canceller of the first embodiment, the description thereof is omitted.

As shown in FIG. 5, the side tone detection unit 105 of the present embodiment includes an absolute value calculation unit 201, a maximum value detection unit 202, an average value calculation unit 301, a threshold setting unit 302, and a threshold comparison unit 303. It consists of.
The operations of the absolute value calculation unit 201 and the maximum value detection unit 202 are the same as those in the first embodiment (steps S200 and S201 in FIG. 6).

The average value calculation unit 301 calculates the average value Fa (t) of the absolute value F (t) of the filter coefficient H (t) calculated by the absolute value calculation unit 201 (step S206). The calculation process of the average value calculation unit 301 is expressed by Expression (4).
Fa (t) = cF (t) / L (4)
C in Expression (4) is a vector having 1 in 1 row and L column as an element, and is expressed by Expression (5).
c = {1, 1, 1,..., 1} (5)

The threshold value setting unit 302 multiplies the average value Fa (t) calculated by the average value calculation unit 301 by a preset constant A (A ≧ 1) to calculate a threshold value G (t) (step S207). . The calculation process of the threshold setting unit 302 is expressed by Expression (6).
G (t) = A · Fa (t) (6)

  The threshold comparison unit 303 compares the maximum value Fm (t) detected by the maximum value detection unit 202 with the threshold G (t) set by the threshold setting unit 302 (step S208), and the maximum value Fm (t) Is larger than the threshold value G (t), it is determined that there is a side sound, that is, the own apparatus is connected to a device such as a telephone that generates the side sound (step S209), and the maximum value Fm (t) is If it is equal to or less than the threshold value G (t), it is determined that there is no side sound, that is, the apparatus is not connected to a device that generates side sound (step S210). Then, the threshold comparison unit 303 outputs the detection result of the presence or absence of side sounds to the switch unit 106 (step S211).

  As described above, in the present embodiment, a device such as a telephone that generates a side sound using not the fixed threshold G but the threshold G (t) corresponding to the average value of the filter coefficients of the variable filter unit 102 By determining whether or not there is a connection, it is possible to detect the presence or absence of a side sound even when a device with an uncommon side sound level is connected to the own apparatus. Other effects are the same as those in the first embodiment.

[Third Embodiment]
Next, a third embodiment of the present invention will be described. FIG. 7 is a block diagram showing the configuration of a side tone canceller according to the third embodiment of the present invention. The sidetone canceller 402 according to this embodiment is obtained by adding a filter coefficient reset unit 401 to the sidetone canceller according to the first embodiment or the second embodiment.
The variable filter unit 102, the filter coefficient update unit 103, the subtraction unit 104, the side sound detection unit 105, and the switch unit 106 are the same as those in the first embodiment or the second embodiment, and thus description thereof is omitted. .

The filter coefficient reset unit 401 is connected from a state in which its own device (hands-free device) including the sidetone canceller is connected to a device that generates a sidetone (a device such as a telephone connected to a telephone connection terminal). When the state is shifted to a state where it is not performed, all the filter coefficients of the variable filter unit 102 are cleared to zero. FIG. 8 is a block diagram showing the configuration of the filter coefficient reset unit 401, and FIG. 9 is a flowchart showing the operation of the filter coefficient reset unit 401.
The filter coefficient reset unit 401 includes a level calculation unit 501, a level calculation unit 502, a constant multiplication unit 503, and a comparison unit 504.

The level calculation unit 501 calculates the time average level P (t) of the reception signal e (t) after the sidetone cancellation, which is the output of the subtraction unit 104 (step S300 in FIG. 9). The time average level P (t) is calculated by the equation (7).
P (t) = (1-b) · P (t−1) + b · | e (t) | (7)
However, b is a preset constant less than 1, and as b is closer to 1, the time constant of the time average of level calculation becomes longer. | X | represents taking the absolute value of x.

The level calculation unit 502 calculates the time average level Q (t) of the reception signal y (t) before the sidetone cancellation (step S301). The time average level Q (t) is calculated by the equation (8).
Q (t) = (1-b) · Q (t−1) + b · | y (t) | (8)

  If there is a side tone and the side tone canceller is working, the signal level of the received signal e (t) after canceling the side tone is lower than the received signal y (t) before canceling the side tone. The relationship P (t) <Q (t) is established. In this state, when the side sound suddenly disappears, the level of the pseudo side sound signal y ′ (t) of the variable filter unit 102 is the time average level Q (t) of the reception signal y (t) before the side sound cancellation. Therefore, the relationship P (t)> Q (t) is established. By utilizing this phenomenon, it is detected that the own device including the sidetone canceller shifts from a state where it is connected to a device such as a telephone that generates a sidetone to a state where it is not connected.

The constant multiplier 503 multiplies the preset constant d (d ≧ 1) by the time average level Q (t) calculated by the level calculator 502 (step S302).
The comparison unit 504 compares the output d · Q (t) of the constant multiplication unit 503 with the output P (t) of the level calculation unit 501 (step S303), and based on the output d · Q (t) of the constant multiplication unit 503. If the output P (t) of the level calculation unit 501 is larger, all the filter coefficients of the variable filter unit 102 are cleared to 0 (step S304).

As described above, when it is detected that the own apparatus including the sidetone canceller shifts from a state where it is connected to a device that generates a sidetone to a state where it is not connected, the filter coefficient of the variable filter unit 102 is set to 0. As a result, the pseudo side sound that is added as an unnecessary sound when the device is connected to the device that generates the side sound is not connected, before the filter coefficient is learned. In addition, it can be prevented from occurring.
As described above, according to the present embodiment, in addition to the effects of the first embodiment or the second embodiment, it is not connected from a state where it is connected to a device that generates a side sound. The pseudo side sound added as an unnecessary sound when the state is shifted can be quickly erased.

  The sidetone cancellers 101 and 402 according to the first to third embodiments can be realized by a computer having a CPU, a storage device, and an external interface, and a program for controlling these hardware resources. . In such a computer, the CPU executes the processes described in the first to third embodiments in accordance with a program stored in the storage device.

  The present invention can be applied to a side-tone canceller that eliminates side-tones in a hands-free call or the like.

  DESCRIPTION OF SYMBOLS 101,402 ... Side-tone canceller, 102 ... Variable filter part, 103 ... Filter coefficient update part, 104 ... Subtraction part, 105 ... Side-tone detection part, 106 ... Switch, 201 ... Absolute value calculation part, 202 ... Maximum value detection part , 203 ... fixed threshold value comparison unit, 301 ... average value calculation unit, 302 ... threshold value setting unit, 303 ... threshold value comparison unit, 401 ... filter coefficient reset unit, 501 ... level calculation unit, 502 ... level calculation unit, 503 ... constant multiplication Part, 504... Comparison part.

Claims (10)

A variable filter procedure for filtering a transmission signal to be transmitted to a call partner with a set filter coefficient;
A subtraction procedure for subtracting the output signal obtained by the variable filter procedure from the received signal from the other party;
Based on the transmission signal and the output signal obtained by the subtraction procedure, the filter coefficients of the variable filter procedure are sequentially set so that the mean square of the side tone, which is the transmission signal component included in the reception signal, becomes small. A filter coefficient update procedure to be updated;
A sidetone detection procedure for detecting the presence or absence of the sidetone based on a filter coefficient of the variable filter procedure;
When the detection result of the sidetone detection procedure is that there is a sidetone, the output signal obtained by the subtraction procedure is selected and output, and when the detection result is that there is no sidetone, the received signal is A sidetone canceling method comprising: a switching procedure for selecting and outputting. The sidetone canceling method according to claim 1,
The sidetone detection procedure is:
An absolute value calculation procedure for calculating an absolute value of a filter coefficient of the variable filter procedure;
A maximum value detection procedure for obtaining a maximum absolute value of the filter coefficient;
A preset fixed threshold value is compared with the maximum value, and it is determined that there is a side sound when the maximum value is larger than the fixed threshold value, and it is determined that there is no side sound when the maximum value is equal to or less than the fixed threshold value. And a fixed threshold comparison procedure. The sidetone canceling method according to claim 1,
The sidetone detection procedure is:
An absolute value calculation procedure for calculating an absolute value of a filter coefficient of the variable filter procedure;
A maximum value detection procedure for obtaining a maximum absolute value of the filter coefficient;
An average value calculation procedure for calculating an average value of absolute values of the filter coefficients;
A threshold setting procedure for setting a value obtained by multiplying the average value by a preset constant as a threshold;
Comparing the threshold value with the maximum value, determining that there is a side sound when the maximum value is larger than the threshold value, and a threshold comparison procedure for determining that there is no side sound when the maximum value is less than or equal to the threshold value. A side-tone canceling method comprising: In the sidetone canceling method according to any one of claims 1 to 3,
The method further comprises: a filter coefficient reset procedure for setting a filter coefficient of the variable filter procedure to 0 when the side sound is present and the side sound is absent. In the sidetone canceling method according to claim 4,
The filter coefficient reset procedure includes:
A first level calculation procedure for calculating the level of the output signal obtained by the subtraction procedure;
A second level calculation procedure for calculating the level of the received signal;
A constant multiplication procedure for multiplying the level of the received signal by a preset constant;
When the level of the output signal obtained by the subtraction procedure is compared with the level of the output signal obtained by the constant multiplication procedure, and the level of the output signal obtained by the subtraction procedure is greater, the variable filter A sidetone canceling method comprising a comparison procedure for setting a filter coefficient of the procedure to 0. Variable filter means for filtering a transmission signal to be transmitted to the other party with a set filter coefficient;
Subtracting means for subtracting the output signal of the variable filter means from the received signal from the other party;
A filter that sequentially updates the filter coefficient of the variable filter means based on the transmitted signal and the output signal of the subtracting means so that the mean square of the side tone that is the transmitted signal component included in the received signal is reduced. Coefficient updating means;
Side sound detecting means for detecting the presence or absence of the side sound based on a filter coefficient of the variable filter means;
When the detection result of the sidetone detection means is a side sound, the output signal of the subtraction means is selected and output, and when the detection result is no side sound, the reception signal is selected. A side-tone canceller comprising switch means for outputting. The side-tone canceller according to claim 6,
The side sound detection means includes
Absolute value calculating means for calculating the absolute value of the filter coefficient of the variable filter means;
Maximum value detecting means for obtaining the maximum absolute value of the filter coefficient;
A preset fixed threshold value is compared with the maximum value, and it is determined that there is a side sound when the maximum value is larger than the fixed threshold value, and it is determined that there is no side sound when the maximum value is equal to or less than the fixed threshold value. A side-tone canceller comprising: a fixed threshold value comparison means. The side-tone canceller according to claim 6,
The side sound detection means includes
Absolute value calculating means for calculating the absolute value of the filter coefficient of the variable filter means;
Maximum value detecting means for obtaining the maximum absolute value of the filter coefficient;
An average value calculating means for calculating an average value of absolute values of the filter coefficients;
Threshold setting means for setting a value obtained by multiplying the average value by a preset constant as a threshold;
From the threshold value comparison means that compares the threshold value with the maximum value, determines that there is a side sound when the maximum value is larger than the threshold value, and determines that there is no side sound when the maximum value is less than or equal to the threshold value. A side-tone canceller characterized by In the side-tone canceller according to any one of claims 6 to 8,
The sidetone canceller further comprising filter coefficient resetting means for setting the filter coefficient of the variable filter means to 0 when the sidetone is present and the sidetone is absent. The side-tone canceller according to claim 9,
The filter coefficient reset means includes
First level calculating means for calculating the level of the output signal of the subtracting means;
Second level calculating means for calculating the level of the received signal;
Constant multiplication means for multiplying the level of the received signal by a preset constant;
The level of the output signal of the constant multiplying means and the level of the output signal of the subtracting means are compared. When the level of the output signal of the subtracting means is larger, the comparison is performed with the filter coefficient of the variable filter means being 0. A side-tone canceller characterized by comprising:

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